Serum++
Harmor++
Biohazard++
Zeta+2++
Papen Predator RE++ (I have the Reason "RE" version; I'd imagine the VST is equally awesome)
I don't know about FL's included synths, but I know Reason has MORE than enough for someone just starting out. I can only assume that anything more than the bare bottom (fruity loop?) edition of FL would have enough to get you started. You need to understand how oscillators work, the three/four different waveforms (sine, triangle, square/pulse, tooth) and how they combine (e.g. supersaw, detune), you need to understand things like the difference between additive and subtractive synthesis, etc. All of this can be accomplished with either the synths that come with most DAWs, or also with a couple of free synths (pluginboutique.com has a whole section just on free stuff, also try varietyofsound.wordpress.com/vst-effects/ for excellent free effects).
Sampling is also huge, especially if you prefer the "nasty" heavily-processed style of bass in DnB (e.g. Neuro). Massive is the classic go to for mashing up samples and sound generation, tho Serum has something going on, too. Papen also just did something, I think. But until you are already able to make basic growls, wubs, etc. with the synths + sampler that came with your system, don't bother shelling out the £100+ yet. I would also look into one tasty, fun, true analog synth (this means something independent, as I'm unaware of 100% analog synths designed to be plugged into a PCI-e slot). There are many good options for comparatively little money, though of course buying real physical gear will always cost more. I really like my Moog Minitaur, but here again, you should know enough about how synths work before you go shopping, so you already know what kind of synth would most appeal to you (the Minitaur cannot really do leads, for example; it's special "Taurus-style" filter has been limited by the factory because Moog doesn't feel it sounds good in the upper registers. For Bass-heavy genres like DnB and Psytrance, this issue doesn't bother me personally).
I'm not even signed or anything, so I'm sure people who are further along can help you even more. But just to get to the point of knowing what you don't know takes a lot of work and time. And time. And a bit more work. And some weed. And time.
Good luck; don't forget to post the occasional track in the subforum here.